Seduction Tapehead w/ CS4 1 channel out 1 channel distorted.

[galyons]

My Seduction is not feeling well. The left channel is  distorted and the right  is out.  I bought the unit from Doc when he was closing out the in-house use Seductions. So, I don't have the "I built it experience" to help me out on this one.  It has the CS4 upgrade.  I have the Seduction manual, but not the CS4 manual, so some of the terminal designations do not match up.  The resistance checks seem to be fine.

The tubes are fine, both tested and then replaced with new 6922's.  (I had Amperex 7308's in originally, but put in new EH 6922's till issue is resolved.  I don't want to risk the 7308's)

The outboard pair of Led's on the CS4 do not light.  All of the other Led's are lit. 

The voltage check issues are:
27/37   70vdc  56/130vdc
29/39   70vdc  56/130vdc
39/40   70vdc  56/130vdc
A1/B1  135vdc 66/90vdc
A6/B6    70vdc  56/130vdc

The voltage at the 2 75K 1watt resistors is 128V inboard leg
I can't read the resistance value in circuit , I get out of limit, but the outboard LED's light when the DVM leads are on both legs of the outboard resistor.

All of the 1/8 watt resistors are 130 +/- 1vdc

All of the outer legs of the CCS transistors read 129 +/- 1vdc

The center legs are 1) closest to 1 watt resistors  56.5vdc
2) 65.6vdc
3) 130vdc
4) 90.2vdc

So any thoughts on what has happened and how I would fix it?  Let me know if other tests need to be done.

TIA,
Cheers,
Geary

[galyons]

Wow! Almost 5 months, no ideas?     Are my measurements confusing?   I tried test matching with my Seduction Phono.    I think the issue may be with the CS4.   I think I have a couple of bad LED's on the board.  They voltage drops too much across them and they fail a basic diode test.  Short of other thoughts, I will give the Queen a buzz tomorrow to get some new LED's. (And, hopefully, a CS4 disc.)

I really would  like to get the R2R back into the system. 

Cheers,
Geary

[Paul Birkeland]

Holy cow, how did we miss this one?

Try swapping tubes to see if the dim LED's on the C4S board move.

I think you have a weak tube.  Do they both grow with roughly the same amount of light?

-PB

[galyons]

Thanks PB! I wasn't feeling the love!     

 I tested and swapped tubes, so I think that the tubes are OK. 

The 2 LED's are  light-less, as far as I can tell.  They were mounted dome down, so not nearly as bright as the LED's on my S/Phono where the LED's are mounted dome up.   So they may be gasping a last few photons!  (I would normally go into the Monty Python "Dead Parrot" routine here, but I'll refrain!) 

The voltage comes into the board and goes through the 2 lit LED's, but drops by more than half through the unlit LED's.  I pulled one and it failed the diode test.    The voltage goes through the lit LED's fine, with virtually no loss.

So that was how I came to my conclusion that those 2 LED's are bereft of life.  So do you think I should call the Queen?

Cheers,
Geary

[Paul Birkeland]

You can call the Queen, but I have yet to have one of our LED's just fail out of nowhere (generally they die from being soldered and desoldered).

I'd ask for a pair of LED's, a 2N2907, and two MJE-350's, just to cover the bases.

-PB

[galyons]

I may have very well killed  one I since I de-soldered it to test "out of circuit".  I  have never had one fail and I have a gazillon of them in the various BH kit I own.  But I am hoping that this is an outlier situation and the new LED's solve the problem.  I will ask for the transistors, as well. I agree, prudent to be safe, at this point.

Thank you for the help!

Cheers,
Geary

[Paul Joppa]

Just a reminder to be careful with the orientation of the replacement LEDs. Yes, I'm sure you're sure the originals were oriented correctly - but a partial voltage drop is consistent with a backward diode in avalanche mode. And it is really, really hard to tell the orientation even installed dome-down. I'm paranoid as heck about it, and I still eff it up all the time.